The production of ethers by the reaction of an isoolefin and an alcohol are well known commercial operations. There are many detailed descriptions of processes for the production of such ethers, in particular, methyl tertiary butyl ether (MTBE) and methyl tertiary amyl ether (TAME). These ethers have long been known as useful octane blending agents for gasoline motor fuels due to their high octane number (RON) of about 120. More recently ether compounds as gasoline blending components have been highly valued as supplying oxygen to meet reformulated gasoline requirements. Processes for the production of MTBE and TAME by reacting methanol with isobutylene or isoamylene, respectfully, are among the most widely known processes for the production of such ethers.
Processes for the production of such ethers have suffered from a shortage of the necessary isoolefins for reaction with the alcohols to provide products. Feedstreams for etherification processes typically consist of a wide variety of olefinic and paraffinic isomers. It is known that the available feedstock can be increased by the isomerization and dehydrogenation of paraffins and the skeletal isomerization of olefins. Methods for the dehydrogenation of paraffins, in particular isoparaffins, are known in the art as are processes for the skeletal isomerization of normal olefins to isoolefins. Since many of the olefinic and paraffinic isomers of any given carbon number have relatively close boiling points, separation of the isomers in an efficient manner to enhance the production of ether as well as the conversion of unreacted products to additional reactants have been difficult. Methods for the various separations have included adsorptive separations as well as extractive distillations. Unreacted olefins and paraffins have also been used as feed to alkylation units. There is a need for etherification and isomerization process arrangements that simplify the separation of olefinic and paraffinic isomers to provide product and reactants.
Since the butane isomers are not converted in the etherification or isomerization zone various process steps and schemes have been proposed for the efficient rejection of the these paraffins. Again the close boiling points of the saturated and unsaturated isomers can lead to a problem of olefin loss by the carryover of these hydrocarbons with the usually vented paraffins. To prevent this carryover processes have employed high efficiency extractive distillation, adsorption, or other methods to separate the normal butenes from butane.
It is an object of this invention to provide a process arrangement for the rejection of butane from combination isomerization and etherification processes for the conversion of C.sub.4 hydrocarbons.
It is a further object of this invention to provide a butyl ether product and a high purity butene-1 product in a simplified etherification and isomerization arrangement and without the use of extractive distillation.